Poly(amino acid) has been widely utilized in drug delivery, tissue engineering and biomedical materials. The biomaterials based on poly(glutamic acid) are usually modified via copolymerization with other monomers such as L-aspartic acid to improve the uncontrolled degradation rate. The ring-opening homo- and co-polymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and β-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) were carried out in solution by using triethylamine (TEA) as initiator. The BLG-NCA homopolymerization could take place even at －30οC and molecular weight of poly(γ-benzyl-L-glutamate) decreased with increasing polymerization temperature. The BLA-NCA polymerization did not occur at －10οC and was needed to be carried out at 25οC to improve the polymerization. Poly(γ-benzyl-L-glutamate) and poly(β-benzyl-L-aspartate) with unimodal molecular weigh distribution and weight average molecular weight (Mw) of 32100 and 4000 could be obtained at 25οC. The copolymers of γ-benzyl L-glutamate and β-benzyl L-aspartate with unimodal molecular weight distribution and Mw ranging from 5600 to 24600 could be prepared. The useful copolymers of poly(L-glutamic acid-co-L-aspartic acid) were further prepared by removal of benzyl groups.